A New Family of Constrained Codes with Applications in Data Storage

Abstract

Line codes make it possible to mitigate interference, to prevent short pulses, and to generate streams of bipolar signals with no direct-current (DC) power content through balancing. They find application in magnetic recording (MR) devices, in Flash devices, and in optical recording devices. This paper introduces a new family of fixed-length, binary constrained codes, named lexicographically-ordered constrained codes (LOCO codes), for bipolar non-return-to-zero signaling. LOCO codes are capacity achieving, the lexicographic indexing enables simple, practical encoding and decoding, and this simplicity is demonstrated through analysis of circuit complexity. Experimental results demonstrate a gain of up to 10% in rate achieved by LOCO codes with respect to practical run-length-limited codes designed for the same purpose. Simulation results suggest that it is possible to achieve channel density gains of about 20% in MR systems by using a LOCO code to encode only the parity bits of a low-density parity-check code before writing.